For many years, condensation particle counters (CPC) have been used in various settings to detect and count submicrometer particles (or other suspended aerosol elements). Condensation particle counters operate by “growing” the particles into larger droplets by condensing onto the particles a working fluid vapor. Typically, room air (or other gas(es) being monitored) is/are drawn through an inlet area into a chamber located inside a saturator block. A working fluid evaporates into a gas stream being tested or measured, saturating the stream with working fluid vapor. From the saturator, the test gas is drawn into a condenser tube and cooled sufficiently to supersaturate the vapor. Vapor condenses onto the particles, forming aerosol droplets much larger than the particles. From the condenser, the gas stream containing the grown particles or droplets passes an optical detector that senses the aerosol droplets traveling through a viewing volume defined by a laser and associated optics. For further information regarding this type of instrument, reference is made to U.S. Pat. No. 4,790,650 (Keady), U.S. Pat. No. 5,118,959 (Caldow et al.), and U.S. Pat. No. 7,407,531 (Flagan et al.), all of which are incorporated herein by reference.
The saturator block of a CPC can include at least in part a saturator block or wick that is made of a material with a certain porosity. When the bottom of the saturator block is set in a pool of working fluid at ambient pressure, the liquid is drawn or wicks up into the porous material and fills the pores. However, at equilibrium the working fluid may not fill every pore and some pores may remain filled with air.
When a CPC experiences a change in differential inlet pressure below ambient pressure, air in the pores may expand and push the working fluid out of the wick. The working fluid that has been pushed out can drain down the surface of the saturated wick in a thin film, and if not reabsorbed into the wick, can reach the saturator base and drip into the inlet of the CPC. When enough working fluid accumulates in the inlet, the sample air flow is forced to bubble through the liquid in the inlet, which in turn generates high concentrations of working fluid particles that are detected upstream in the CPC optics, leading to false counts.
There exists a need therefore for an apparatus and/or system for preventing CPC working fluid from being pushed out of the wick and/or for preventing working fluid that is pushed out of the wick from accumulating in the inlet area of the CPC to an amount where it may be aerosolized and detected as “false counts” by the CPC optics.